Project 2 wlW test the hypothesis that in non-ICSF most stones do not originate as overgrowths on duct of Bellini crystal plugs. We have established that in ICSF, calcium oxalate stones form as overgrowths on interstitial deposits of hydroxyapatite (Randall's plaque) in patients with large stone burden requiring PNL. We will extend this approach to patients with ICSF and smaller stones who will be treated with URS utilizing digital instrumentation in order to investigate the generalizability of our observation of calcium oxalate overgrovi/th on plaque and, further, that plaque abundance correlates with histologic and metabolic data, as well as clinical stone events. We will also investigate the discordance between acidic bulk urine and tubular deposits of apatie or urate in stone formers with ileostomy and non-bariatric enteric hyperoxaluria utilizing a novel fiberoptic pH microsensor to test the hypothesis that injured BD have local acidification defects enabling deposition of crystals favoring a more alkaline millieu. Finally, we will compare CaP stone content of calyceal stones with a papillary injury scoring system testing the hypothesis that more severely damaged calyces will have more impairment of tubular acidification resulting in a higher percentage of CaP content in stones produced.